This invention relates to an electrophotographic printing machine, and more particularly concerns an improved apparatus for supporting a moving photoconductive belt.
In an electrophotographic printing machine, a photoconductive belt is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive belt is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive belt selectively discharges the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive belt corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive belt, the latent image is developed by brining a developer mix into contact therewith. Generally, the developer mix comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive belt. The toner powder image is then transferred from the photoconductive belt to a copy sheet. Finally, the copy sheet is heated to permanently affix the toner particles thereto in image configuration. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and has been further amplified and described by many related patents in the art.
Existing photoconductive belt supports utilize two or more rolls for drive and support. Each roll may cause belt run-out, and lateral skew, as well as producing frictional resistance to belt steering. Furthermore, particles may be entrapped between the belt and rolls resulting in belt scoring. Herinbefore precise elastomerically coated rollers, sealed bearings, mounting the rollers in self-aligning assemblies and/or providing for accurate mounting of the rollers and relatively complex and/or low latitude tracking systems were required. Alternatively, it is desirable to employ a single drive roller and one or more air posts. Generally, an air post has an arcuate portion with a pressurized fluid, such as air, being supplied to the region between the arcuate portion and the photoconductive belt. The pressurized fluid is supplied through porous regions in the arcuate portion or via small apertures therein. These apertures are generally located just inside the tangent lines between the belt and the arcuate portion or directly under the pressurized load. This results in forming a gap between the photoconductive belt and the arcuate portion. The gap is a minimum at the tangent exit and entry regions. Most of the pressurized fluid tends to escape from the side marginal portions. Fluid consumption may be reduced by sealing the side marginal portions. This minimizes the required fluid flow and volume so as to reduce the cost associated with the system.
In addition to employing rows of holes or porous regions in the walls of the air post, it is frequently advantageous to form a pattern of grooves in the surface of the post. This latter structure requires relatively few large diameter apertures conduct the pressurized fluid to the grooves. A system of this type employs large diameter holes which are less likely to become clogged. Holes of this type are easier to generate and the spacing between adjacent holes is not very critical. This system requires less power and is more economical to manufacture.
Accordingly, it is a primary object of the present invention to improve the pneumatic system furnishing pressurized fluid for supporting a belt moving in a pre-determined path.